Experimental And Aseismic Research Of SMAFDB And Design Method Of Self-centering Bracing Based On Energy

NiTi shape memory alloy(NiTi SMA)has unique selfcenterning property,high damping property and high cost performance.The hyperelastic strain of NiTi SMA is usually between 6%and 8%.When the material strain is higher than this value,the crystal of the constituent material becomes martensitic phase,which will produce obvious strain hardening phenomenon and easily cause material fracture.In this paper,a new type of NiTi SMA-friction damper brace(SMAFDB)is formed by connecting NiTi SMA selfcenterning damper and friction damper in series.Compared with other braces,this kind of brace has more excellent characteristics.It will show the same effect as the selfcenteming damper at the level of small and medium earthquakes,forming high damping and selfcenterning effect.In large earthquakes,excessive deformation will be borne by friction damper,which will not damage SMA material,and improve the energy consumption capacity of the brace.In order to comprehensively evaluate the seismic level of the brace,through the analysis of the expected effect of the brace,through the quasi-static low cycle reciprocating loading test,combined with the theoretical analysis,and using the OpenSees seismic engineering analysis software,a series of numerical simulation of the seismic effect of the brace is carried out.Three groups of quasi-static loading tests are carried out,including friction damper,selfcenteming damper and SMA friction damper.The hysteretic behavior and energy consumption level of dampers(bracings)are studied.The performance of the brace and the effect of the predicted brace performance are discussed.The test results have achieved the expected performance of the brace.At the same time,according to the test data,using the finite element analysis software OpenSees,the damper(brace)model is established using selfcenterning material model,and the simulation static analysis is carried out.The test results of the brace are consistent with the simulation test results of the numerical model,which can be used in the engineering model application.In order to study the anti-seismic effect of the new SMA-friction damper brace,the anti-seismic effect of the model of the new brace is analyzed in OpenSees software,and compared with the anti-seismic effect of the common brace and the special anti-seismic effect,the following three groups of simulation tests are carried out respectively.A buckling restrained braced(BRB)steel frame model and a SMA-friction damper braced(SMAFDB)steel frame are established in OpenSees software(1),and the nonlinear dynamic simulation is carried out under three groups(frequent earthquake,design basis earthquake and rare earthquake)of 60 seismic waves with different risk levels,To determine the seismic effect of the brace.(2)A steel frame model of SMA friction damper brace(SMAFDB)and a steel frame of SMAB are established,and the seismic response of these two kinds of steel frames are compared in the above three groups of seismic waves to determine the selfcenterning effect and seismic effect of the brace.(3)A single degree of freedom steel frame model is established to analyze the seismic effect of dampers under different periods and ductility,which can be used for reference in the next engineering application.Finally,an energy-based seismic design method of SMA brace(SMAB)is proposed by using the cumulative ductility spectrum and hysteretic energy spectrum.A three-story and a six story SMA braced frame(SMABF)is designed in OpenSees.The effectiveness of the design method is verified by the seismic analysis of the three groups of seismic waves.